# convert to factorial(x); tofactorial(binomial(n_,k_)) := n!/((n-k)!*k!); tofactorial(gamma(x_)) := (x-1)!; tofactorial(gamma(x_)/gamma(y_)) := (-1)^(y-x)*(-y)!/((-x)!); tofactorial(psi(x_)/gamma(x_)) := (-1)^(-x+1)*(-x)!; tofactorial(fallingfactorial(m_,n_)) := m!/((m-n)!); tofactorial(risingfactorial(m_,n_)) := (m+n-1)!/((m-1)!);